Polyacrylamide hydrogel as a soft tissue filler endoprosthesis

ABSTRACT

A hydrogel is obtained by combining acrylamide and methylene bis-acrylamide, radical initiation and washing with pyrogen-free water or saline solution to give less than 3.5% by weight polyacrylamide, based on the total weight of the hydrogel. The hydrogel may be used as a soft tissue filler endoprosthesis. Also disclosed is a method of filling a soft tissue in a mammal using the endoprosthesis, and a prosthetic device comprising the polyacrylamide hydrogel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 09/938,669, filed Aug. 27, 2001, which claims the benefit,under 35 U.S.C. § 119(e), of Provisional Application No. 60/228,081,filed Aug. 25, 2000. Both applications are hereby incorporated byreference in their entirety.

FIELD OF INVENTION

The invention relates to a polyacrylamide hydrogel used as a prostheticdevice for soft tissue augmentation such as facial cosmetic surgery, lipaugmentation and soft tissue correction of the body. The hydrogelcomprises less than 3.5% polyacrylamide solid weight content and pyrogenfree water or saline solution.

BACKGROUND OF THE INVENTION

The success of plastic or reconstructive surgery depends to a greatextent on the physical properties of the materials utilized. They mustmost certainly be biocompatible, stable and non-toxic but they must alsohave physical properties that mimic the bodily tissue they arereplacing, as in reconstructive surgery, and mimic the bodily tissue inthe proximity of the endoprosthesis, as in cosmetic surgery.

Natural and synthetic polymers such as collagen, soya, glycerol,silicone, polyvinylpyrolidone and hyaluronic acid have been utilized asendoprostheses. Materials used for endoprostheses generally try toimitate the natural soft tissue and are intended to be safe to thehealth of the patient. Materials such as collagen are re-absorbed intothe body over short periods of time. Silicone and soya have encounteredserious safety issues. There is currently a need for a safe, stable,biocompatible material that possesses the physical properties to mimicsoft tissue.

Polyacrylamide gels have also been disclosed. WO 96/04943 relates to abiocompatible hydrogel containing 3.5 to 6.0% cross-linkedpolyacrylamide. However, WO 96/04943 teaches that concentrations below3.5% make the hydrogel unstable.

GB 2114578 relates to a polyacrylamide gel for medical and biologicalpurposes containing 3 to 28% polyacrylamide with the remainder of themass of the gel comprised of a physiological solution. According to GB2114578, the prospective utility in the polyacrylamide gel lies in themanufacture of artificial crystalline lenses (contact lenses), a densebase in growing microorganisms. GB 2114578 discloses the preparation ofgels having 4.0 to 20.0%, 5.0 to 18.0% and 6.0 to 15.0% solid weightcontent.

U.S. Pat. No. 5,658,329 relates to an implantable endoprosthesiscomprising a shell filled with a polyacrylamide gel comprising 2 to 20%polyacrylamide by weight and a viscosity range of 15 to 75 Pas.

Formacryl® polyacrylamide is a soft-tissue endoprosthesis consisting of5% reticulated polyacrylamide polymer and 95% apyrogenic watercommercialised as an injectable device for medical and dental use tocorrect congenital or acquired deficits such as wrinkles, lines andscars. It is to be implanted with a syringe in the hypodermis.

U.S. Pat. No. 5,306,404 relates to a process for preparingpolyacrylamide gel plates for electrophoresis.

WO 99/10021 relates to an injectable, biocompatible hydrogel comprising0.5 to 10% polyacrylamide and an antibiotic or antiseptic. WO 99/10021is directed to the solving the problem of sappuration and rejection ofthe gel in its use an endoprosthesis.

SUMMARY OF THE INVENTION

In a first aspect, the invention relates to a hydrogel for use as a softtissue filler endoprosthesis said hydrogel obtainable by combiningacrylamide and methylene bis-acrylamide, radical initiation; and washingwith pyrogen-free water or saline solution so as to give less than 3.5%by weight polyacrylamide, based on the total weight of the hydrogel.

In a second aspect, the invention relates to the use of a hydrogelcomprising less than 3.5% by weight polyacrylamide, based on the totalweight of the hydrogel, for the preparation of an endoprosthesis forsoft tissue filling. Similarly, the invention relates to a method offilling soft tissue in a mammal comprising administering anendoprosthesis wherein the endoprosthesis comprises a hydrogelcomprising less than 3.5% by weight polyacrylamide, based on the totalweight of the hydrogel.

A further object of the invention is to provide a prosthetic device forsoft tissue augmentation said device being injectable and comprising apolyacrylamide hydrogel said hydrogel being obtainable by combiningacrylamide and methylene bis-acrylamide; radical initiation; and washingwith pyrogen-free water or saline solution, so as to give less than 3.5%by weight polyacrylamide, based on the total weight of the hydrogel;

GENERAL DESCRIPTION OF THE INVENTION

The term “facial” in intended mean of relation to all areas of the face,such as but not exclusively, the cheeks, the jaw, the neck, theforehead, under the eyes, the head area, and the nose.

The term “body contouring” is intended to mean cosmetic orreconstructive surgery wherein soft tissue is augmented in order tocorrect a cosmetic or non-cosmetic defect in the soft tissue in thebody, excluding the face, lips, breasts and penis. The present inventionrelates to facial corrections, lip augmentation, and body contouring.

The term hydrogel relates to the polyacrylamide polymer of the inventioncomprising less than 3.5% polyacrylamide and at least 95% pyrogen-freewater or saline solution whereas the term endoprosthesis relates to thehydrogel present in the body.

The polyacrylamide hydrogel of the invention is obtainable by thepolymerisation of the monomers acrylamide andN,N′-methylene-bis-acrylamide under radical initiation, followed bywashing of the polymer with pyrogen-free water or saline solution. Thewashing of the polymer results in a swelling of the gel, due toabsorption of the pyrogen-free water or saline solution by the polymer.The swelling of the hydrogel influences the solid weight content of thegel, i.e. the amount of polymeric material, polyacrylamide. The solidweight content of the hydrogel influences, at least in part, thephysical (rheological) properties of the hydrogel and thus the abilityto mimic human tissue when used as an endoprosthesis.

The present investigators have prepared a hydrogel having the desiredTheological properties to act as a soft tissue filler endoprosthesiswhich is completely atoxic, stable, and non-resorbable. The presentinvestigators have developed the hydrogel to be particularly amenablefor use as an endoprosthesis for facial cosmetic or reconstructivesurgery, for body contouring and for lip augmentation or reconstruction.The hydrogel of the present invention is not directed for use as anendoprosthesis for breast or penis augmentation.

A first aspect of the invention relates to a hydrogel for use as a softtissue filler endoprosthesis said hydrogel obtainable by combiningacrylamide and methylene bis-acrylamide in amounts so as to give lessthan 3.5% by weight polyacrylamide, based on the total weight of thehydrogel; radical initiation; and washing with pyrogen-free water orsaline solution. Typically, the hydrogel is obtained by said combiningacrylamide and methylene bis-acrylamide in a molar ratio of 150:1 to1000:1. The hydrogel obtained in this manner has a structural formula asshown in FIG. 1, is sterile, has transparent or colourless appearanceand has a pH in the range of 6.5 to 9.0, typically 7.0 to 9.0.Furthermore the hydrogel of the invention is stable to oxygen, highpressure, high and low temperatures, enzymes and bacteria.

The invention thus relates to the use of a hydrogel comprising less than3.5% by weight polyacrylamide, based on the total weight of thehydrogel, for the preparation of an endoprosthesis for soft tissuefilling. Given the hydrogel of the invention is directed for use as anendoprosthesis, it must be stable. Furthermore, given the hydrogel ofthe invention is directed for use as an endoprosthesis for selectedparts of the human anatomy, the hydrogel typically comprises at least0.5% by weight polyacrylamide, based on the total weight of thehydrogel, preferably at least 1.0% by weight polyacrylamide, morepreferable at least 1.5% by weight polyacrylamide, such as at least 1.6%by weight polyacrylamide, based on the total weight of the hydrogel.Typically, the hydrogel of the present invention may have a solid weightcontent of 1.5, 1.6, 1.7 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6,2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.5% polyacrylamide, based onthe total weight of the hydrogel.

In a preferred embodiment of the present invention, the hydrogelcomprises about 1.9 to 2.9% by weight polyacrylamide, based on the totalweight of the hydrogel. The hydrogel typically further comprises atleast 95% by weight pyrogen-free water or saline solution, preferablypyrogen-free water. In a preferred embodiment, the hydrogel comprises atleast 96% by weight pyrogen-free water or saline solution, preferablypyrogen-free water, more preferably at least 97% by weight pyrogen-freewater or saline solution, preferably pyrogen-free water, such as 95%,95.5%, 96%, 96.5%, 97%, or 97.5% by weight pyrogen-free water or salinesolution, preferably pyrogen-free water.

A suitable saline solution has an osmolarity similar to that ofinterstitial fluid. Suitable saline solutions include but are notlimited to the group selected from 0.25-1% aqueous sodium chloride, aRinger-Lockart solution, an Earle solution, a Hanks solution, an Eaglemedium, a 0.25-1% glucose solution, a potassium chloride solution, and acalcium chloride solution. In a preferred embodiment, the salinesolution is an about 0.8-1% aqueous sodium chloride solution, such as a0.8, 0.9 or 1% aqueous sodium chloride solution.

Pyrogen-free water or saline solution is used for the washing process.The washing process serves, in part, to remove all but trace amounts ofthe monomers acrylamide and N,N′-methylene-bis-acrylamide. Thesemonomers are toxic to the patient as well as detrimental to thestability of the hydrogel. The washing process is preferably such thatthe concentrations of the monomers acrylamide andN,N′-methylene-bis-acrylamide are below 50 ppm, more preferably below 40ppm, such as below 30 ppm, particularly preferably below 20 ppm,typically below 10 ppm, most preferably less than 5 ppm.

The solid weight content of the hydrogel of the present invention isessentially completely contributed by the polyacrylamide andN,N′-methylene-bis-acrylamide with residual contribution by theinitiator. The hydrogel is substantially free of any other polymericcontent.

As stated, the hydrogel of the invention is biocompatible, atoxic,non-allergenic, non-resorbable, chemically inert and stable to oxygen,high pressure, high and low temperatures, enzymes and bacteria. In theevent that the hydrogel is exposed to excessive amounts of UV light, thephysical features of the hydrogel are altered and is converted into aglue-like substance. Advantageously, this substance is also non-toxic.

Upon administration of the hydrogel, a thin layer of connective tissuesurrounds the endoprosthesis, enabling the endoprosthesis to become astable part of the connective tissue. Due to the bio-stability of thehydrogel and the thin layer of connective tissue, the endoprosthesis maybe easily removed from the patient when placed in the subcutaneous area.This advantage is at least in part due to the stability of the hydrogelwhich in turn is at least in part due to the washing process.

Several factors affect the rheological properties of the hydrogel, suchas the relative amount of monomer used, the relative amount ofinitiator, the temperature, the time of polymerisation, and otherparameters of the polymerisation process, as well as the washingprocess. Thus, the polymerisation process may provide a hydrogel with anarray of viscosities having a solid weight content of less than 3.5%.The invention is directed to a hydrogel as a soft-tissue fillerendoprosthesis and thus the hydrogel preferably has a viscosity tailoredto the soft-tissue it is intended to mimic. The hydrogel of theinvention is typically for use as an injectable endoprosthesis forcosmetic or reconstructive surgery of the face, cosmetic orreconstructive surgery of the body (body contouring), and augmentationor reconstructive surgery of the lips.

The hydrogel of the invention may be injectable or implantable into thesubcutaneous layer of the epidermis, preferably the hydrogel isinjectable.

In one embodiment of the invention, the endoprosthesis is for use infacial cosmetic or reconstructive surgery and the hydrogel has a complexviscosity of about 2 to 100 Pas, preferably about 5 to 90 Pas, such asabout 5 to 60 Pas, such as about 10 to 60 Pas. Most preferably, theendoprosthesis for use in facial cosmetic or reconstructive surgery wasplace by means of injection of the hydrogel.

Depending on the condition and region of the epidermis of the face wherethe soft-tissue filler is required (e.g. chin as opposed to cheek), theviscosity of the hydrogel may vary. Accordingly, the hydrogel may be foruse in facial cosmetic or reconstructive surgery and have a complexviscosity of about 2 to 20 Pas, preferably about 2 to 18 Pas, such asabout 2 to 15 Pas or 2 to 10 Pas, more preferably 2 to 7 Pas, mostpreferably 3 to 5 Pas.

In typical embodiments, the endoprosthesis may be for uses in correctionof facial contour deformities due to aging, acne, trauma, surgery,infection or congenital deformities. The facial features typically inneed of correction are, for instance, the cheekbones, nasolabial folds,glabellar frowns, depressed contours of the mouth, the chin, the size orshape the lips, as well as other soft tissue deficiencies of the face.The hydrogel restores the skin contours correcting soft tissue contourdeformities of the face such as wrinkles and folds.

The hydrogel may serve for the preparation of an injectable hydrogel forlip enhancement or correct an array of aesthetic defects caused bycongenital, traumatic or aging alterations.

As stated, invention relates to the use of the hydrogel for thepreparation of an endoprosthesis for the filling of soft tissue fillingselected from the soft tissue of the face and lips and soft tissue ofthe body. The hydrogel of the invention directed for use in the cosmeticor reconstructive surgery of the body (body contouring), preferably hasa complex viscosity of about 5 to 50 Pas, preferably about 7 to 40 Pas,most preferably about 7 to 30 Pas.

In the embodiment wherein the hydrogel is used in the preparation of anendoprosthesis for lip augmentation or lip reconstruction the hydrogelpreferably has a complex viscosity of about 2 to 10 Pas, more preferably2 to 7 Pas, most preferably 3 to 5 Pas.

The elasticity module is an alternative physical characteristic of thehydrogel indicative, in part, of the degree of cross-linking of thehydrogel according to the present invention. Typically, the degree ofcross-linking is such that the hydrogel has an elasticity module of notless than 10 Pa, such as not less than 25, 30, 31, 32, 33, 34 or 35 Pa,such as not less than 38 Pa. The gel may be characterized in that it haselasticity module from about 10 to 700 Pa, such as about 35 to 480 Pa.

A further object of the invention is to provide a prosthetic device forsoft tissue augmentation said device being injectable and comprising apolyacrylamide hydrogel said hydrogel being obtainable by combiningacrylamide and methylene bis-acrylamide in amounts so as to give lessthan 3.5% by weight polyacrylamide, based on the total weight of thehydrogel; radical initiation; and washing with pyrogen-free water orsaline solution.

The prosthetic device of the invention preferably comprises a hydrogelcomprising at least 0.5% by weight polyacrylamide, based on the totalweight of the hydrogel, preferably at least 1% by weight polyacrylamide,more preferable at least 1.5% by weight polyacrylamide, such as at least1.6% by weight polyacrylamide, based on the total weight of thehydrogel. Typically, the hydrogel comprises about 1.9 to 2.9% by weightpolyacrylamide, based on the total weight of the hydrogel. Theprosthetic device comprises the hydrogel which typically comprises atleast 95% by weight pyrogen-free water or saline solution, preferablypyrogen-free water.

A further aspect of the invention relates to a method of filling softtissue comprising administering an endoprosthesis wherein theendoprosthesis comprises a hydrogel comprising less than 3.5% by weightpolyacrylamide, based on the total weight of the hydrogel. The hydrogelmay be as described supra.

In an alternative embodiment of the invention, the prosthetic devicecomprises cells, such as stem cells. Polyacrylamide provides anexcellent template and matrix for cell growth. Although the hydrogel ofthe invention allows, in itself, for a thin layer of connective tissuefrom the body of the patient to surround the device, the use of cells incombination with the hydrogel of the invention for the preparation ofthe device allows for cellular engraftment to the surrounding tissue.

The method of the invention typically comprises administering thehydrogel of the invention by injecting the hydrogel, into thesubcutaneous layer of the skin in the embodiments wherein theendoprosthesis is for facial cosmetic or reconstructive surgery or bodycontouring. In the embodiment wherein the endoprosthesis is for lipaugmentation or lip reconstruction, the injecting is above the muscletissue of the lip.

The method may comprise of more than one injection so as to cover thedesired area or to achieve the desired affect.

As stated, an alternative embodiment of the invention comprisesadministering the hydrogel of the invention in combination with cells,such as stem cells to allow for cellular engraftment of the prostheticdevice.

The gel to be injected is typically stored in a syringe suitable forinjecting the required amount for a single session treatment. Dependingon the afflicted area, the amount of gel and thus volume of the syringemay vary, such as a syringe with a volume of 0.25-25 mL, such as asyringe selected from 0.5 mL, 0.7 mL, 1.0 ml, 1.5 mL. 2.0 mL, 2.5 mL,5.0 mL, 7.5 mL, 10 mL, 12.5 mL. 15 mL, 20 mL and 25 mL. Obviously, theprosthetic device for use in facial surgery or lip augmentation beprovided in a syringe in an array of volumes, typically lower in volumethan the volumes provided for by the prosthetic device for bodycontouring. For instance, the device for lip augmentation may beprovided in volumes of 0.5 ml or 0.7 mL or 1 mL whereas the device forbody contouring may be provided in volumes of 2 mL, 5 mL, or 10 mL.These are purely illustrative examples and are not intended to limit thescope of the invention in any way—the device of the invention may beprovided in any volume required to perform the method.

As stated, the hydrogel is highly biocompatible. The method of theinvention does not comprise of adding an antibiotic, analgesic oranti-inflammatory agent to the hydrogel.

In the preferred embodiment wherein the method comprises the injectionof the endoprosthesis, the injection comprises the use of a syringe witha thin gauge needle such as a 21-29 G needle. The necessary amount ofthe gel is injected subcutaneously in a retrograde manner by injectingthe gel while withdrawing the needle. After the injection is performed,a light manipulation may be required in order to obtain an evendistribution of the gel. Post-operative oedema may be treated with localpacking of ice and mild pain and redness may be experienced during thefirst 2-3 days after injection.

In the embodiment wherein the method comprises injection of theendoprosthesis for lip augmentation or facial correction the needle ofthe syringe is typically particularly thin, such as a 25-29 G needle.For body contouring, the needle of the syringe may be in the range 21-23G.

EXAMPLES Example 1

Preparation of Hydrogel

The gel is a polyacrylamide gel manufactured by a polymerisation of themonomers of acrylamide and N,N′-methylene-bis-acrylamide. The finishedproduct may have different viscosities.

The hydrogel has the empirical formula [C₃H₅NO]_(x)[C₇H₁₀N₂O₂]_(y) andthe structural formula as shown in FIG. 1

The hydrogel typically contains approximately 95% water. Theconcentration of the monomers acrylamide andN,N′-methylene-bis-acrylamide has been shown to be less than 10 ppm andis adequate for the desired stability of the final product, often lessthan 5 ppm.

The finished product must conform with respect to pH, absence of heavymetals, refractive index, stability, absence of pyrogens, and must besterile, practically inert, and be substantially free of monomers.

Preparation 1.1

The synthetic preparation suitably involves the following operations:

-   1. Two mixtures, A1 and A2, are prepared. A1 comprises water,    acrylamide, N,N′-methylene-bis-acrylamide,    N,N,N′,N′-tetramethylene-ethylene-diamine (TEMED). A2 comprises    water and ammonium persulphate;-   2. The two mixtures are combined in the following ratio: 1990 mL of    A1 and 10 mL of A2 and kept at 45° C. and degassed with nitrogen for    20 seconds;-   3. The reaction mixture is cast into several 100 mL beakers;-   4. Polymerisation is allowed to occur for 0.5 to 1.5 hours;-   5. The gel is demolded;-   6. Residual monomers are extracted and with equilibration in WFI    water for 92 hours, changing the water several times, typically 8    times during the 92 hours;-   7. The purified gels are homogenised by grinding with an vertically    oscillating grid;-   8. The syringe is filled with the homogenised gel material;-   9. Autoclavation of the syringe

A typical method for preparing the hydrogel may be summarised as:

Preparation 1.2

Process summary. The gel is prepared by mixing an aqueous monomersolution of acrylamide and N,N′-methylene-bis-acrylamide as cross-linkerwith N,N,N′,N′-tetramethylene ethylene diamine (TMED) as co-initiatorand ammoniumpersulfate (APS) as free-radical initiator (redox-system).By degassing a bulk solution with nitrogen polymerisation starts. Afterfinal polymerisation the gel transferred into a washing tank with nettrays onto which the gel is placed. During water washing the gel swellsand monomer residues are extracted. The swollen gel is fed and evacuatedin a filling unit having the gel delivered in a syringe, which isautoclaved.

Two alternate formulations have been prepared, a lower- and a higher-endviscosity formulation. Both formulations have a solid weight content ofless than 3.5% and a complex viscosity in the range of 2 to 50 Pa s,typically between 3 and 20 Pa s.

TABLE 1 Chemical constituent lower end viscosity higher end viscosityacrylamide 502 g 547 g N,N′-methylene-bis- 2.2 g 4.6 g acrylamide TMED3.0 g 2.6 g APS 5.4 g 5.0 g Non-pyrogenic water Add 10 litre Add 10litre

The above are typical preparations of the hydrogel and may be adjustedwithin certain ranges.

Preparation 1.3

Polyacrylamide Formulations from Inline Cross-Linking Process

A particularly interesting method of preparing the hydrogels of theinvention involves an inline cross-linking process. Two individual andeventually degassed flows, one being a pre-mix of acrylic amide,bis-methylene acryl amide (the cross-linker) and TEMED, the other beingthe AMPS initiator solution, are pumped into a static mixer for mixing,chemical initiation and subsequent extrusion downstream into a pipereactor made of Teflon or steel in which the polymerisation occurs.Washing of the gel is simplified due to high surface area of gel fromreactor.

By selecting monomer, cross-linker and initiator concentrations andtheir relative molar ratios, and by regulating the two flow rates andthe polymerisation temperatures, it is possible to produce gels that arevarying in degree of crosslinking and in solids content.

Preparation 1.4

The reagents were combined in ratios described in Tables 2, 3 and 4, andwashed as described in the Tables (with pyrogen-free water unlessindicated otherwise) to give low, medium, and high viscosityformulations. Hydrogels with solid weight contents between 0.5 and 25%polyacrylamide were prepared.

TABLE 2 Process parameters and features of resulting gel: low viscosityformulations lv1 lv2 lv3 lv4 lv5 lv6 lv7 ^(d) lv8 ^(e) washing time a)19.5 73.75 92 94.3 72.8 93.6 93.9 (hrs) dry matter^(i) 2.55 2.08 2.632.87 2.89 3.15 3.68 3.17 (%) 2.36 2.58 2.67 2.82 2.90 3.57 3.52 2.09molar ratio b) 976 700 488 366 3239 488 488 AM:bisAM molar ratio 252 252253 251 252 249 252 252 AM + BISAM: TEMED molar ratio 298 299 298 298298 299 298 298 AM + BISAM: APS residual c) 89 5 2.97 2 5 1, 4 0.97monomer in ppm elasticity G′ 0.16 5.23 14.3 26.6 57.05 71.7 39.2 28.5 inPa 20.1 viscosity .045 .88 2.35 4.37 9.1 11.5 6.29 4.55 in Pa s 3.30gelation time liquid highly 12 2 2 2 2.5 2.5 (min) viscous liquid lv9lv10 lv11 lv11 lv12 washing time 121 96.4 (hrs) dry matter 2.18(5.10)^(f) (10.2)^(f) (10.1)^(f) (20.2)^(f) (%) molar ratio 701 701 488488 488 AM:bisAM molar ratio 252 252 252 504 2016 AM + BISAM: TEMEDmolar ratio 298 298 298 596 2385 AM + BISAM: APS residual 0.97 monomerin ppm elasticity G′ 28.5 11.1 (911)^(g) (1240)^(g) (9460)^(g) in Paviscosity 4.55 1.8 (145)^(g) (197)^(g) (1505)^(g) in Pa s gelation time3.17 0.00 1.21 3.5 ^(h) (min) ^(a)material was liquid so washing was adilution ^(b)infinite ^(c)since washing was not an extraction but adilution, the residual monomer was merely decreased by the dilutionfactor (508 ppm to 254 ppm). ^(d)casting and washing done using 0.9%NaCl aqueous solution ^(e)casting with water; washing done using 0.9%NaCl aqueous solution ^(f)pre-wash values - washing typically reducesvalue by 30–55% ^(g)pre-eash values - washing typically reduces value by20–40% ^(h)highly notch sensitive ^(i)variations in values may be due tomeasurement performance techniques or to location in the batch fromwhich sample was taken

TABLE 3 Process parameters and features of resulting gel: mediumviscosity formulations mv1 mv2 mv3 mv4 mv5 washing time 97 211.5 96 94.890.3 (hrs) dry matter 3.14 2.49 3.25 3.29 3.22 (%) molar ratio 310 310290 289 289 AM:bisAM molar ratio 252 252 252 251 252 AM + BISAM: TEMEDmolar ratio 299 299 299 299 299 AM + BISAM: APS residual 1.6 1.5 monomerin ppm elasticity G′ 108.5 129 133.5 in Pa viscosity 17.4 20.6 21.30 inPa s gelation time 2.5 2.5 2.18 (min)

TABLE 4 Process parameters and features of resulting gel: high viscosityformulations hv1 hv2 hv3 hv4 hv5 washing time 119.5 516 122 95.5 116.7(hrs) dry matter 3.47 2.5 3.56 3.83 3.42 (%) molar ratio 260 260 260 260260 AM:bisAM molar ratio 315 315 604 313 314 AM + BISAM: TEMED molarratio 376 376 755 375 376 AM + BISAM: APS residual 0.2 monomer in ppmelasticity G′ 343 274 314.5 in Pa viscosity 54.7 43.65 50.1 in Pa sgelation time 2.18 2.18 7.5 (min)

Example 2

Method of Administration

-   a) The injection of the gel may be performed under local    anaesthesia, but for correction of wrinkles and folds, local    anaesthesia is not necessarily required. For lip augmentation,    anaesthesia through the nerve block is recommended.-   b) The procedure must be performed under sterile conditions.    Pharmaceuticals are not to be injected into the gel-   c) The gel is pre-filled in sterile syringes of 1 mL with luer-lock    and should be injected subcutaneously with a thin gauge needle, e.g    27 G. Needles should be CE-marked.-   d) Inject the necessary amount of the gel subcutaneously in a    retrograde manner by injecting the gel while withdrawing the needle.    A patient record label is part of the packaging and is removable and    to be attached to the patient record to ensure that the product is    traceable.-   e) After the injection is performed, a light manipulation may be    performed in order to obtain an even or desired distribution of the    gel. The injected gel will form a stable, soft part in the    connective tissue and will give long lasting cosmetically    satisfactory appearance.-   f) Further injection sessions may be performed to achieve the    desired affect.    Post-Operative Procedures

If oedema occurs, ice packs may be applied locally. Exposure to directsunlight or extreme cold or heat is advised until the initial swellingand redness has been resolved.

Adverse Events/Side Effects

It is not uncommon for patients to develop some pain within the first2-3 days post-operatively. A mild degree of oedema will occur in somepatients during the first 2-3 days after injection.

The correct injection technique is crucial for the final result of thetreatment and to be performed by authorised personnel.

The gel is sterilised (such as by moist heat or autoclavation). In theeven that the package is damaged or opened but unused, sterility may becompromised and the contents should be discarded. Re-sterilisation isnot advisable.

Example 3

Clinical Experience

-   1) Approximately 900 patients underwent facial corrections with the    gel. The overall cosmetic results were excellent and the frequency    or adverse events was 0.02% (Kovanskaya V. A.; Scienctific    conference, 13-16 Oct. 2000).-   2) A total of 150 adults undergoing correction of the contour    deformities of the face were treated with the injectable gel. The    amount of gel injected was from 0.2 to 11 mL.

Scheduled visits took place at a screening day (3 days prior to day 0),day 0 (first injection), day 7, day 28, month 3, month 6 and at end ofstudy visit month 12 and underwent a physical examination and vitalsigns test, pregnancy test, blood and serum analysis, hematology test,immunology test, urine analysis, concomitant treatment, side effect andevents analysis, cosmetic outcome analysis by patient and surgeon aswell as completing a questionnaire according to the schedule of Table 5.

Results

The overall rating of the outcome of the surgery was from very good togood from both the patients and the surgeon. In some instances, thepatients wanted to continue the treatment and receive furtherinjections. Several surgeons remarked spontaneously on the questionnairethat the patients were happy with the result and that the gel was easyto handle and administer.

The gel was very well tolerated. Only a few side-effects were recordedand the Adverse Events oedema and inflammation were reported by thepatient. The Adverse Events resolved spontaneously after a few days.

TABLE 5 Day 0 Screening (Facial month (at least −3 correction) Day 7 Day28 month 3 month 6 12 days) pre-op post-op ±1 day ±2 days ±7 days ±7days ±7 days information/ X informed consent physical X X X examinationvital signs X X X X X X pregnancy X test blood and sampling X X X serumanalysis Haematology sampling X X X Immunology sampling X X X Urineanalysis X X X Concomitant X X X X X X X treatment side effects X X X XX X and events questionnaire X X X X X X (complaints) Cosmetic outcomePatient X X X X Surgeon X X X X

1. A method of filling soft tissue comprising administering a hydrogelas an endoprosthesis to an area in need thereof, said hydrogelcomprising about 0.5 to less than 3.5% by weight polyacrylamide, basedon the total weight of the hydrogel; wherein the polyacrylamide iscrosslinked polyacrylamide; said hydrogel consisting essentially of apolymer of said crosslinked polyacrylamide, and at least 95% by weightpyrogen-free water or saline solution, and less than 50 ppm ofacrylamide and methylene-bis-acrylamide monomers, and wherein thehydrogel has an elasticity module from about 10 to 700 Pa and a complexviscosity from about 2 to 100 Pas, and wherein said endoprosthesisconsists essentially of said hydrogel.
 2. The method according to claim1, wherein the endoprosthesis does not comprise an antibiotic, analgesicor anti-inflammatory agent.
 3. The method according to claim 1, whereinthe hydrogel is obtainable by combining acrylamide and methylenebis-acrylainide in a molar ratio of 150:1 to 1000:1.
 4. The methodaccording to claim 1, wherein the hydrogel comprises at least 1.0% byweight polyacrylamide, based on the total weight of the hydrogel.
 5. Themethod according to claim 1, wherein the hydrogel comprises from about2.0 to 3.0% by weight polyacrylamide, based on the total weight of thehydrogel.
 6. The method according to claim 1, wherein the soft tissue issoft tissue of the face; wherein the endoprosthesis is for facialcosmetic or reconstructive surgery; and wherein the hydrogel has acomplex viscosity of about 2 to 20 Pas.
 7. The method according to claim1, wherein the soft tissue is soft tissue of the body; wherein theendoprosthesis is for cosmetic or reconstructive surgery of the body(body contouring), and wherein the hydrogel has a complex viscosity ofabout 5 to 50 Pas.
 8. The method according to claim 1, wherein the softtissue is soft tissue of the lip; wherein the endoprosthesis is for lipaugmentation or lip reconstruction; and wherein said hydrogel has acomplex viscosity of about 2 to 10 Pas.
 9. The method according to claim1, wherein the administering comprises injecting the hydrogel.
 10. Themethod according to claim 9, wherein the endoprosthesis is for facialcosmetic or reconstructive surgery or body contouring and the injectingis into the subcutaneous layer of the skin.
 11. The method according toclaim 9, wherein the endoprosthesis is for lip augmentation or lipreconstruction and the injecting is above the muscle tissue of the lip.12. The method according to claim 9, further comprising administeringcells for cellular engrafment to the surrounding tissue.
 13. The methodaccording to claim 1, wherein the hydrogel comprises at least 1.5% andless than 3.5% by weight polyacrylamide, based on the total weight ofthe hydrogel.
 14. The method according to claim 1, wherein the softtissue is soft tissue of the face; wherein the endoprosthesis is forfacial cosmetic or reconstructive surgery; and wherein the hydrogel hasa complex viscosity of about 2 to 18 Pas.
 15. The method according toclaim 1, wherein the soft tissue is soft tissue of the face; wherein theendoprosthesis is for facial cosmetic or reconstructive surgery; andwherein the hydrogel has a complex viscosity of about 2 to 15 Pas. 16.The method according to claim 1, wherein the soft tissue is soft tissueof the face; wherein the endoprosthesis is for facial cosmetic orreconstructive surgery; and wherein the hydrogel has a complex viscosityof about 2 to 10 Pas.
 17. The method according to claim 1, wherein thesoft tissue is soft tissue of the face; wherein the endoprosthesis isfor facial cosmetic or reconstructive surgery; and wherein the hydrogelhas a complex viscosity of about 2 to 7 Pas.
 18. The method according toclaim 1, wherein the soft tissue is soft tissue of the face; wherein theendoprosthesis is for facial cosmetic or reconstructive surgery; andwherein the hydrogel has a complex viscosity of about 3 to 5 Pas. 19.The method according to claim 1, wherein the soft tissue is soft tissueof the body; wherein the endoprosthesis is for cosmetic orreconstructive surgery of the body (body contouring), and wherein thehydrogel has a complex viscosity of about 7 to 40 Pas.
 20. The methodaccording to claim 1, wherein the soft tissue is soft tissue of thebody; wherein the endoprosthesis is for cosmetic or reconstructivesurgery of the body (body contouring), and wherein the hydrogel has acomplex viscosity of about 7 to 30 Pas.
 21. The method according toclaim 1, wherein the soft tissue is soft tissue of the lip; wherein theendoprosthesis is for lip augmentation or lip reconstruction; andwherein said hydrogel has a complex viscosity of about 2 to 7 Pas. 22.The method according to claim 1, wherein the soft tissue is soft tissueof the lip; wherein the endoprosthesis is for lip augmentation or lipreconstruction; and wherein said hydrogel has a complex viscosity ofabout 3 to 5 Pas.
 23. The method according to claim 12, wherein thecells are stem cells.
 24. The method according to claim 1, wherein thehydrogel has an elasticity module of not less than 25 Pa.
 25. The methodaccording to claim 1, wherein the hydrogel has an elasticity module ofnot less than 38 Pa.
 26. The method according to claim 1, wherein thehydrogel has an elasticity module of about 35 to 480 Pa.